1. Field of the Invention
The present invention relates to an apparatus for and a method of cleaning or otherwise wet-treating a wafer. More particularly, the present invention relates to a cleaning/etching apparatus having an internal tank and an external tank that receives the cleaning/etching liquid that overflows the internal tank, and to the pumping of the cleaning/etching liquid from the external tank.
2. Description of the Related Art
The number of thin films formed on a wafer to manufacture a semiconductor device has been increasing to meet the demand for more highly integrated semiconductor devices. Thus, when semiconductor devices are manufactured, each thin film-forming process is followed by a process of cleaning the wafer to decrease the risk of defects and process malfunctions.
Generally, the wafer cleaning process entails dipping the wafer into a chemical solution or deionized water (hereinafter, cleaning liquid) such that metallic impurities, organic contaminants, or native oxides are removed from the surface of the wafer.
A conventional cleaning apparatus for performing the cleaning process comprises a cleaning tank containing the cleaning liquid into which the wafer is dipped, and a pump that pumps the liquid chemical from the cleaning tank. The pump includes a bellows which moves axially from side to side to pump the cleaning liquid, and right and left sensors disposed at both sides of the pump. The sensors are operative to turn on and off according to the reciprocating movement of the bellows. In the conventional cleaning apparatus, a determination of whether the pump is operating normally is made based on the time interval at which the right and left sensors are turned on and off. That is, if the time interval at which the right and left sensors are turned on is longer or shorter than a preset time interval, the pump is considered to be malfunctioning and the operation of the wafer cleaning apparatus including that of the pump is shut down.
However, if the operation of the wafer cleaning apparatus is abruptly shut down, the cleaning process may be stopped while wafers are submerged in the cleaning liquid in the cleaning tank. As a result, impurities remaining in the liquid may be absorbed into the surface of the wafer. Also, if the wafers are being wet etched using the cleaning apparatus, the wafers will not be etched by the desired amount.